Blankets, particularly quilts, should protect the human body. They create a zone between the body and the surrounding air which impedes an exchange of heat between the body and the surroundings and thereby reduces the radiation of heat from the human body, thereby preventing an undercooling of the resting body.
Depending on the ambient temperature, it may be desired that more or less of the heat produced by the human body escape through the blanket. If the ambient temperature is low and the heat gradient is thus relatively high, as for example in the winter, then the blanket should retain as much of the heat produced by the body as possible. If, on the other hand, the ambient temperature is relatively high, as for example in the summer, then it may even be desired that as much heat as possible be carried away from the human body.
As a rule, the retention of heat is essentially achieved by providing an immovable air volume above the human body, i.e. the effect is for the most part achieved by a stationary air cushion, whereby use is made of the fact that air has a low coefficient of thermal conduction.
This means that a blanket, in particular a quilt, should allow a transmission of heat that is inversely proportional to the temperature drop. This is not possible with conventional blankets.
It was therefore proposed to use different blankets in the summer than in the winter or fall and spring which is why one speaks of so-called "summer blankets", "winter blankets" and "fall blankets".
"Winter blankets" and "fall blankets" are designed in such a way that if possible there are no thermal bridges. Thus, instead of normal quilting seams, webs are used, which ensure that the top sheet is the same distance, if possible, from the bottom sheet in the area of the stitching as in the area between the stitching. Fall blankets and in particular winter blankets are also fuller or thicker in order to be able to hold as large an air volume as possible. In the summer these blankets are too warm, i.e. heat builds up under the blanket since the heat produced by the person is not carried away due to the low heat conductivity and the relatively low temperature drop in the summer.
"Summer blankets" are very light, and can also have quilting seams forming otherwise undesired thermal bridges. These so-called thermal bridges allow the heat to pass through very easily. If necessary, a summer blanket should also be able to absorb or let through the perspiration given off by the human body.
It has also been proposed to design a quilt as a blanket system such that several individual blankets can be combined into one overall blanket to form one blanket which is thicker in accordance with the individual blankets. However, this blanket is then also correspondingly heavier.
In both known proposals, the use of two blankets is provided, whereby the second blanket must be stored when it is not being used.
A so-called web blanket in which the outer surfaces of the blanket are joined together by means of webs also on the outer edges of the blanket is known from German U-8.704.127.8. The blanket is divided into a plurality of chambers by the inner webs. Closable openings can be provided in at least one such outer web, to allow filling material, which can be down, synthetic filling, wool and the like, to be fed in. The inner webs are designed in part as discontinuous webs in such a way that the openings of the inner webs also permit access to the internal chambers. Since down can also be used as filling material in this blanket, the closures in the outer webs must be designed to be down-proof, i.e. they are sewn shut after the blanket is filled. Once manufacturing of this blanket is finished, its properties are no longer changed. The filling material can be evenly distributed in the blanket through the discontinuous inner webs.
A so-called coffered blanket is known from German A-3 147 023. Here continuous and intersecting inner webs are provided which divide the blanket into a plurality of chambers. It is proposed that continuous easily closable opening devices, such as zippers, be provided essentially over the length of the webs extending in one direction. To replace, empty, and fill the blanket, an edge seam of the blanket is opened and subsequently sewn up so that the cover is down-proof. To fill and empty the blanket, the zippers disposed on the inner webs can be opened and closed.
Thus, filling or emptying the two aforenamed blankets entails a great deal of work, in particular the outside opening of the covering must always be sewn up again.
From German A-491 524 and Swiss A-658 177 blankets are known which have a casing with longitudinal chambers or pockets into which toroidal or square cushions can be inserted or removed. Thus, in the summer, cushions with a different design can be used than in the winter. Both blankets are basically casings for taking up several smaller blanket parts which can also be used separately.